The goals of this project are to elucidate protein kinase C (PKC) signaling mechanisms that contribute to lung cancer initiation and maintenance and translate these mechanistic insights into better prognostic and treatment strategies. We recently identified the atypical PKC? gene PRKCI as a human oncogene in the lung. Furthermore, we find that the mouse PKC? gene Prkci is required for the very earliest steps of lung tumorigenesis induced by oncogenic Kras in vivo. Specifically, Prkci is necessary for Kras-mediated transformation of bronchio-alveolar stem cells (BASCs), the putative cell of origin of Kras-mediated lung tumorigenesis. Genetic disruption of Prkci, or treatment with the PKC9 inhibitor aurothiomalate (ATM), blocks Kras-mediated expansion and morphological transformation of BASC in vitro and in vivo, and lung tumor growth in vivo. Preliminary results suggest that Kras-, Prkci-mediated expansion of BASCs involves induction of the polycomb gene Bmi1. Bmi1 is an epigenetic chromatin modifier/transcriptional regulator implicated in cancer stem cell identity and self-renewal. Like Prkci, Bmi1 is necessary for Kras-mediated BASC expansion and lung tumorigenesis. Based on these preliminary data, we hypothesize that Prkci drives Kras-mediated BASC transformation and lung tumorigenesis, at least in part, through activation of the Bmi1 signaling pathway. We further hypothesize that a similar PKC?-Bmi1 signaling axis plays a critical role in the maintenance, expansion and tumorigenic potential of human lung cancer stem cells. Finally, we hypothesize that ATM will effectively inhibit the self-renewal and tumorigenic potential of human lung cancer stem cells. We will test these hypotheses through completion of two interrelated specific aims. In Aim 1 we will assess the role of the PKC?-Par6-Ect2-Rac1 signaling axis in BASC transformation and dissect the mechanism of crosstalk between PKC? and Bmi1 signaling in these cells. In Aim 2 we will determine the role of PKC? and Bmi1 signaling in the self-renewal and tumor initiating activity of lung cancer stem cells. We will develop and characterize a panel of lung cancer stem cell lines from primary lung tumors. Completion of these studies will provide important new mechanistic insight into oncogenic PKC? signaling in putative lung cancer stem cells, enhance our understanding of Kras-mediated lung tumorigenesis, and assess the efficacy of a novel therapeutic agent that targets a critical oncogenic pathway in lung cancer stem cells. These studies have important implications for PKC? as a therapeutic target and for the use of ATM as a novel therapeutic for the treatment of lung cancer. PUBLIC HEALTH RELEVANCE: Lung cancer is the number one cause of cancer death in the United States. Protein kinase C??(PKC?) is an oncogene, prognostic marker and therapeutic target in lung cancer. This project will elucidate PKC? signaling mechanisms that drive lung cancer stem cell growth and tumor-initiating activity, and determine the efficacy of a novel PKC? inhibitor, aurothiomalate, to block lung cancer stem cell growth and tumorigenicity. Finally, this project will generate novel lung cancer stem cell resources from human lung cancer patients. These tissue resources will be invaluable in the assessment of novel therapeutics targeting these deadly cells.